Process of treating cellulosic bodies



Patented July 6, 1937 UNITED STATES PATENT OFFICE PROCESS OF TREATING CELLULOSIC BODIE James Kai-r Hunt and George Henry Latham,

Wilmington, DeL, assignors to E. I. du Pont de Nemours & Company, poration of Delaware- Wilmington, Del., a cor- 6 Claims.

This invention relates to the art of retarding deterioration of organic materials and more particularly to the stabilizing of cellulose, cellulose manufactures, and chemical derivatives of cellulose. I

It has been discovered that deterioration of the above cellulosic bodies can be effectively retarded by treating them with small amounts of certain stabilizing chemical agents, namely organic and inorganic thiocyanates, especially the latter, of which an example is sodium thiocyanate. V

It has been discovered that, by the addition of thiocyanates to cellulose, certain derivatives thereof, and the manufactures of both, these cellulosic materials are greatly protected against the deteriorating effect of concentrated ultraviolet rays from artificial sources. The thiocyanates also delay to a greater or less extent the deterioration of cellulosic materials which are subjected only to that amount of ultra-violet light ordinarily present in the atmosphere, or which are aged in the absence of light. Briefly, these agents are effective in retarding the deterioration oi cellulosic substances in the presence of light of various types and intensities. However, neither the nature of the deterioration of cellulosic bodies (whether oxidatlve, hydrolytic, or otherwise), nor the way in which the present agents function to prevent it, is entirely clear, and it is not desired to be confined to any theory thereof.

The general object of this invention is to provide methods for retarding the deleterious effects of aging on paper, cellulosic fabrics, and various other cellulosic materials.

A particular object of this invention is to provide methods for decreasing the deterioration, due to ultraviolet rays and other causes, of regenerated cellulose, cellulose ethers, and organic acid esters of cellulose. Either the raw materials or some manufactures thereof, e. g., threads, fabrics, etc., may be treated. Cellulose esters to which the present agents may be advantageously applied are cellulose acetate, propionate, butyrate, isobutyrate, crotonate, acetobutyrate, etc. Examples of cellulose others are methyl cellulose, ethyl cellulose, crotyl cellulose, dodecyl cellulose, benzyl cellulose, glycol cellulose, and cellulose glycolic acid. The cellulose esters and ethers may be of the high or low substituted type, the degree of substitution ranging, for example, from one substituent group for each 8 glucose units up to three substituent groups for each glucose unit.

Another particular object of this invention is to provide methods of retarding the deterioration on aging of various cellulose manufactures included in a group comprising paper, cotton filaments, and woven and knitted fabrics of cotton, linen, ramie, jute, etc.

Other objects and advantages of the invention will be pointed out in the following description or will be apparent from such description.

These objects are accomplished by treating paper, cotton goods, and the other aforementloned cellulosic materials with an organic or inorganic thiocyanate, which compounds have the property of stabilizing the cellulosic material against deterioration on aging under various conditions of light and humidity.

The preservatives of this invention can be expressed comprehensively as chemical compounds having the thiocyanate radical. Suitable specific compounds are thiocyanic acid itself (solid form); sodium, potassium, ammonium, mercury, lead, iron, cobalt, nickel, silver, calcium, aluminum, and other inorganic thiocyanates; and relatively non-volatile organic thiocyanates, e. g., p-hydroxydiphenyl thiocyanate isopropyl thiocyanate, methylene and ethylene thiocyanates, thiocyanacetone, dodecyl thiocyanate, phenyl thiocyanate, alpha and beta naphthyl thiocyanates. So far as is known, any compound having the thiocyanate group will retard the deterioration of cellulosic bodies. There are, however, certain preferred types of agents. The thiocyanate should first be relatively non-volatile in order to be retained for long periods of time; the low molecular weight organic thiocyanates, for example, have a tendency to volatilize in time under common conditions of use. The thiocyanate should be soluble so that it may be readily applied; the heavy metal inorganic thiocyanates, for example, are largely insoluble except in reagents which destroy them and/or deleteriously affect the cellulosic body. Of all the agents tested, the water soluble, inorganic thiocyanates, e. g., those of sodium, potassium, lithium, ammonium, diand trivalent iron, etc., are greatly to be preferred because of their greater effectiveness and ease of application.

It has also been observed that thiazoles, e. g., thiazole, amino-thiazole, mercapto-benzothiazole, -ethoxy-l-amino-benzothiazole also retard the deterioration of cellulosic bodies. In this connection, it is interesting to note that some organic thiocyanates are known to rearrange to thiazoles. Thiocyanoacetone, for example, rearranges readily to methyloxythiazole. Thus, it seems possible that the eifectiveness of some organic thiocyanates is actually due, at least in part, to thiazoles, since the latter substances are very effective in themselves. Thiazoles are accordingly included in thm invention.

Our researches have also shown that a few other miscellaneous types of organic sulfur compounds are effective in retarding the deterioration of cellulosic bodies. Among these are the thiophenols such as thiophenol, HS-CGH4-C6H5 (ortho and para isomers), HS-C6H4C6H4SH (the pp isomer), thioaipha-naphthol, and thiobeta-naphthol. Others are the salts and esters 'of aryl sulfonic acids, e. g., sodium, potassium,

and iron benzene sulfonates, and ammonium ptoluene sulfonate, and the sodium, potassium, and ammonium salts of p-nitraniline-o-sulfonic acid and the ethyl, butyl, dodecyl, cyclohexyl, and 9,10- octadecenyl esters of p-toluene sulfonic acid.

The technique of this invention is relatively simple, since in the preferred embodiment of the invention the substance to be treated is simply wetted thoroughly with a solution of the agent in an appropriate solvent, the latter then being allowed to evaporate under conditions where the agent is retained. The solvent should be one which is readily volatile, e. g., below 150, preferably below 100 C. Also, it should not react with the agent, nor affect the cellulosic body in any way. The solvents most used in this invention are water, alcohol, chloroform, acetone, ether, benzene, and the like, the choice depending upon the particular agent used.

The following examples, which are not intended to limit the invention, are illustrative of certain of its more specific embodiments.

Example 1 Strips of woven viscose rayon fabric wide were immersed for 1 hour in a 5% aqueous solution of ammonium thiocyanate. The excess liquid was squeezed out and the treated strips kept side by side with untreated control strips of exactly the same size and shape for 24 hrs. at 25 C. and relative humidity. Two of the controls and two of the treated strips were then tested for elongation and breaking strength on a Scott testing machine. The values obtained-approximately the same for both-were taken as 100%. All the remaining strips, together with the remaining controls, were then exposed to ultraviolet rays under a Cooper-Hewitt quartz mercury vapor lamp in order to accelerate the deterioration of the fabric. All strips were placed at a distance of approximately 24" from the lamp where the temperature was approximately 30 C. Exposure was continued for 72 hrs. Two control strips and two treated strips were removed at the end of 36 and '72 hrs., then stored at 25 C. and 50% relative humidity for 22 hrs., and finally tested for elongation and breaking strength in the same manner as before exposure. At the end of 36 hrs. the untreated control had retained 51.6% and the treated fabric 75.5% of the original strength. At the end of 72 hrs. these figures were 28.3% and 70.0% respectively. By this time, the untreated control was quite weak, readily torn, and practically useless, but the treated fabric, while weakened. slightly, was still in practically its original condition.

Many other substances can be treated in the manner of Example 1. and their deterioration on aging retarded. Among these substances are cellulose acetate, cotton, and paper. While the agent may be applied to the raw materials they are more effectively applied to some manufacture thereof such as acetate rayon (fibers or fabric), thin transparent sheets of regenerated cellulose such as those ordinarily used for wrapping purposes, cotton or rayon textiles, rope, thread, etc. The rate of deterioration is diminished under various conditions of light and humidity.

Example 2 Woven viscose rayon fabric was treated with a 5% aqueous solution of ferric thiocyanate in the same manner as in Example 1. After 36 hrs. exposure to ultraviolet light under the same conditions as in Example 1, the fabric retained 73.5% of its original strength, while the untreated control retained only 51.6%. The corresponding figures at the end of 72 hrs. were 69.0% and 28.3%.

Paper, paper pulp, cotton, thread, cotton tex tiles, and cellulose derivatives may also be rendered more resistant to deterioration by treatment with ferric thiocyanate as in Example 2.

Example 3 Woven viscose rayon fabric is treated with aqueous sodium thiocyanate and the water allowed to evaporate from the fabric. The amount of stabilizer retained was approximately 4% of the weight of the cloth. On exposure to ultraviolet light for 36 hrs., the treated fabric, after test, was found to have retained 58.4% of its original strength. The untreated control retained 51.6% of its original strength. After 72 hrs. the corresponding figures were 54.8 and 28.3%. The advantages to be derived, therefore, from sodium thiocyanate are more evident after the longer period of exposure.

Example 4 Woven viscose rayon fabric was treated with a benzene solution of 5-ethoxy-1-amino-benzothiazole and the benzene allowed to evaporate. The agent was present in an amount of approximately 4% of the weight of the cloth. The treated fabricwas then exposed to ultraviolet light and after 36 hrs., the treated fabric possessed 64.5% of its original strength and the untreated control only 51.6 At the end of '72 hrs., the corresponding figures were 64.5% and 28.3%. This agent is peculiar in its effect. The rate of deterioration gradually becomes less, and finally the treated fabric appears to be completely stabilized against weakening. It is believed that this agent would protect cellulosic bodies for very long periods of time under very drastic conditions, even though it is not as effective for short periods as some of the water-soluble, inorganic thiocyanates such as ferric and ammonium thiocyanates.

An impregnation with about 4% of the stabilizing agent is satisfactory in most instances. The amount required for best results will, however, vary somewhat, depending upon the particular stabilizer used and the particular material treated. As a rule, the quantity of the stabilizer should lie within the range 0.25% to 5.0%, based on the weight of the material treated. Quantities outside this range, are, however, quite practicable and effective, and are by no means excluded.

It will be seen from the preceding examples that impregnated samples of various cellulosic bodies show marked improvement over untreated samples in their resistance to deterioration as induced or accelerated by ultraviolet rays.

It is tobe noted that all systems which are treated in this invention'have a common and distinctive chemical nature irrespective of the processes of this invention. Regenerated cellulose, organic cellulose esters and ethers,- cotton, etc., and various manufactures of all these substances all have a greater or less nuniber of substituted or unsubstituted glucose units joined together in a complex way. It is believed that, because of this fact, this invention is operative in its broader .0 aspects, theagents herein named all exerting some effect on the rearrangement or the breaking up of the bond between these glucose units or building stones, this degradation otherwise producing a physically deteriorated product as evidenced [shy weakening, discoloration, and thelike.

As many apparently widely difi'erent embodiments of this invention may be made without de parting from the spirit and scope thereof, it is to be understood that we do not limit ourselves to 20 the specific embodiments thereof except as defined in the appended claims.

We claim:

1. Textiles derived from a material of the group consisting of cotton, regenerated cellulose, cellu- 25 lose ethers and organic acid esters of cellulose, said textiles having on their fibres a deposit of 0.25% to 5.0% of a soluble thiocyanate selected from a group consisting of alkali metal thiocyanates and ammonium thiocyanate.

2. Cotton textiles having on their fibres a deposit of 0.25% to 5.0% of a soluble thiocyanate, said thiocyanate being selected from a group consisting of alkali metal thiocyanates and ammonium thiocyanate.

3. Regenerated cellulose textiles having on their fibres a deposit of 0.25%- to 5.0% of a soluble thiocyanate, said thiocyanate being selected from a group consisting of alkali metal thiocyanates and ammonium thiocyanate.

4. Textiles of organic acid esters of cellulose having on their fibres a deposit of 0.25% to 5.0% of a soluble thiocyanate, said thiocyanate being selected from a group consisting of alkali metal thiocyanates and ammonium thiocyanate.

5.- Twisted 'strands of regenerated cellulose fibres having. on the fibres a deposit of 0.25% to 6.0% of a soluble thiocyanate, said thiocyanate being selected from a group consisting of alkali metal thiocyanates and ammonium thiocyanate.

6. Twisted strands of cotton fibres having on the fibres a. deposit of 0.25% to 5.0% of a soluble thiocyanate, said thiocyanate being selected from a group consisting of alkali metal thiocyanates and ammonium thiocyanate.

JAMES KARR HUNT. GEORGE HENRY LATHAM. 

